Japanese Unexamined (Kokai) Patent Publication No. 60-175783 and Japanese Unexamined (Kokai) Utility Model Publication No. 62-183082 disclose a typical wobble plate type variable capacity compressing apparatus. The disclosed apparatus is provided with a housing, a cylinder block housed in the housing and a drive shaft arranged so as to axially extend along the longitudinal axis of the housing. The cylinder block has a plurality of cylinder bores that are arranged radially with respect to the axis of the drive shaft and equidistantly to one another. Each of the cylinder bores is communicated with suction and discharge chambers, respectively, via respective reed valves. The suction and discharge chambers of the compressor communicate with a condenser and an evaporator of an air-conditioner of an automobile, respectively.
Each of the cylinder bores receives a piston to be reciprocated therein, and during the suction stroke of the piston, a refrigerant gas sent from the condenser to the suction chamber enters the cylinder bores via the reed valves. The refrigerant gas is subsequently compressed in the cylinder bores during the compressing stroke of the pistons, and the compressed refrigerant is discharged toward the discharge chamber via the reed valves. The compressed refrigerant is then delivered from the discharge chamber of the compressor to the evaporator of the air-conditioning system.
In order to reciprocate the pistons in the cylinder bores, a swash plate is arranged, in a crank chamber of the housing so as, to be slidably engaged with the pistons. Namely, the swash plate is engaged with pistons in a manner such that the rotation of the swash plate causes reciprocation of the pistons. The swash plate is supported and slidable with respect to the drive shaft, and can wobble about an axis perpendicular to the axis of the drive shaft. Further, the angle of inclination of the swash plate can be adjustably changed to control the stroke of the pistons, i.e., the compression capacity of the compressor.
The swash plate is connected to a rotary drive member fixed to the drive shaft via a hinge means to thereby obtain a drive force from the drive shaft, and the hinge means includes a connecting pin element supported by the swash plate. The connecting pin element is engaged in an elongated arcuate hole formed in the rotary drive element. The connecting pin element of the hinge means is moved in the arcuate hole when the angle of inclination of the swash plate is adjusted, and acts as a fulcrum about which the swash plate is moved to change the angle of inclination thereof.
The adjustment of the angle of inclination of the swash plate is performed by changing the pressure level of the refrigerant gas prevailing in the crank chamber, which is in fluid communication with the suction chamber and/or the discharge chamber via an appropriate control valve. Namely, when the pressure level in the crank chamber is lowered by the control valve, pressure acting on the back of each piston is lowered to increase the angle of inclination of the swash plate to thereby expand the stroke of each piston. As a result, the compression capacity of the compressor increases.
On the contrary, when the pressure level within the crank chamber is increased by the control valve, the pressure acting on the back of each piston is accordingly increased to reduce the piston stroke thereby decreasing the angle of inclination of the swash plate. Thus, the compression capacity of the compressor becomes small.
As described above, when the swash plate is moved so as to change the angle of inclination thereof, the movement of the swash plate is conducted with respect to the fulcrum provided by the connecting pin element of the hinge means, and the fulcrum per se moves in response to a change in the angle of inclination of the swash plate. More specifically, in the conventional variable capacity wobbling swash plate type compressor, when the swash plate is moved to the largest inclination angle position thereof, i.e., when the stroke of the pistons is fully extended a specific point of action, where a reaction force due to compression of the refrigerant gas is given by the piston to the swash plate, and the position of the connecting pin element (i.e., the fulcrum of the movement of the swash plate) are in alignment with the center axis of one of the pistons.
Nevertheless, when the angle of inclination of the swash plate is reduced, the connecting pin element is shifted from the aligned position to a position below the above-mentioned specific point of action, and therefore, the reaction force due to the compression of the refrigerant gas produces a rotary moment acting on the swash plate so as to rotate it about the connecting pin element. Namely, the above-mentioned rotary moment provides the swash plate with a further reduction in the angle of inclination thereof, and accordingly, a response to the control operation of the control valve for reducing the angle of inclination of the swash plate to thereby reduce the compression capacity becomes extra-sensitive.
On the contrary, when the control operation is carried out to increase the angle of inclination of the swash plate from the smallest inclination angle position so as to obtain a large compression capacity, a response to the control operation is not sensitive.
Further, in the above-mentioned conventional variable capacity wobbling swash plate type compressor, with the afore-mentioned elongated arcuate hole of the rotary drive element for receiving the connecting pin element it is very difficult to obtain an accurate formation thereof by machining. If an accurate formation of the arcuate hole fails, a change in the top clearance of respective pistons occurs, thereby lowering the compression efficiency. Moreover, an inaccurate formation of the elongated arcuate hole will result in the production of noise during operation of the compressor.